<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
</head>
<body>
<form action="/" id="a">
    <input />
    <input type="submit" value="submit">
</form>
</body>
<script>
    var a = document.getElementById('a');
    a.onSubmit = function(){return null}
</script>
</html>